The present invention relates to an electrostatic copying or reproduction apparatus which is adapted to bifunction as a facsimile transceiver. More specifically, the present invention provides novel means for increasing the apparent resolution of electrostatic copies produced by such an apparatus.
A conventional electrostatic copying machine comprises a photoconductive drum and means for forming a uniform electrostatic charge on the drum. An optical system then radiates a light image of an original document onto the drum to form an electrostatic image. A toner substance is applied to the drum to develop the electrostatic image and form a toner image which is transferred and fixed to a copy sheet to provide a permanent copy or reproduction of the original document.
Such a copying machine can be adapted to bifunction as a facsimile transceiver by providing scanning means such as a photosensor array for producing electrical signals corresponding to an original document. These signals are transmitted to a remote apparatus for reproduction. The copying machine is further provided with electronic imaging means comprising a fiber optic tube array for radiating a light image onto the drum corresponding to electrical signals received from a remote apparatus for reproducing an original document scanned by the remote apparatus.
In television, facsimile and other electronic image transmission it is desired to maximize the apparent resolution of the images. This may be accomplished by subjecting the electrical signals representing the images to a process known in the art as contour compensation. In this process the contrast at the transitions between light and dark image areas is increased, thereby increasing the contrast at the contours or outlines of the image.
Where an original document such as a printed page has a pure white background on which the printed characters are formed, contour compensation is generally unnecessary. However, many original documents have colored, yellowed, gray or otherwise non-white backgrounds which make it difficult to read the printed characters. Contour compensation functions to provide a pure white fringe or outline around the characters or other dark image portions which makes them much more legible.
However, such contour compensation cannot be accomplished in a purely optical imaging system such as found in the typical electrostatic copying machine. In a copying machine adapted to bifunction as a facsimile transceiver as described hereinabove, it is possible to provide contour compensation by disabling the optical system and performing contour compensation on the electrical signals produced by the electronic scanning means. These compensated signals are then applied to the electronic image forming means to form an electrostatic image on the drum. In other words, the optical system is not used to image the drum directly.
Although this expedient does enable contour compensation, it is undesirable in that the actual resolution attainable with the electronic scanning system is lower than that attainable with pure optical scanning. Whereas the optical scanning system provides a continuous image, the electronic scanning system produces a digitized image, the resolution depending on the number of scanning (and corresponding light emitting) elements per unit length in the arrays. At the present state of the art, the resolution produced by digitized scanning using a finite number of elements is lower than that produced by direct optical scanning.